The experience of God was largely what theology was about, so I don't see how the subjects are mutually exclusive or that "testimonials" qualify as history rather than anecdote from the past.
It was the living experience of the living God that inspired St Athanasius and St Gregory of Nazianzen, for instance, in their defense of the Trinity. Their theology was their testimonials:
In Gregory’s view, Christian theology involves and represents a dynamic, lived relationship between God and the theologian, and so it begins not with abstract information about God—as if this could ever be acquired neutrally—but with the transformation of the theologian within the horizon of God’s presence and activity in the world, as it is recognized and celebrated in the life of the Church. It is a constant refrain in Gregory’s work that spiritual progress and right belief unavoidably go together. In other words, Gregory’s doctrines of God and of the human person intrinsically involve each other; as Jean Plaginieux observes, it is impossible to separate Gregory’s doctrine of God from his doctrine of the means by which God is known. Gregory’s doctrine of the Trinity thus includes the theologian’s own situation with respect to God, and theology is a real illumination by which the theologian is initiated into the divine mystery in concrete and far-reaching ways. It is here, Gregory insists, that we must begin.
Beeley, Christopher A. – Gregory of Nazianzus on the Trinity and the Knowledge of God [Oxford Studies in Historical Theology, 2008, p.64]